For a storage apparatus providing a data storage area to an external apparatus such as a host apparatus, a storage virtualization mechanism has been increasingly utilized. With use of the storage virtualization mechanism, the storage apparatus provides the external apparatus with not only a hard disk drive (hereinafter “HDD”) included in the apparatus itself, but also a virtual logical device (Virtual logical DEVice, hereinafter “VDEV”). The VDEV is a virtual unit storage area and is provided based on a physical storage area provided by an HDD included in another external storage apparatus externally coupled to a disk controller (hereinafter “DKC”) in the storage apparatus itself.
Such a virtualization mechanism enables dynamic allocation of storage areas according to a storage capacity required by the external apparatus, rather than previously allocating storage areas to the external apparatus in a fixed manner. Thus, hardware resources of the storage apparatus can be effectively utilized. Examples of such a storage virtualization mechanism are disclosed in Patent Citations 1 to 3, for example.
However, the virtualization mechanism has a problem that all of the VDEVs provided by the external storage apparatus cannot be utilized when failure occurs in the DKC of the storage apparatus, for example. In order to solve this problem, for example, Patent Citation 4 proposes a configuration using a dual-DKC system for an external apparatus, the system including two DKCs coupled to the external apparatus through alternate path connection.    Patent Citation 1: Japanese Patent Application Laid-open Publication No. 2006-285876    Patent Citation 2: Japanese Patent Application Laid-open Publication No. 2007-72538    Patent Citation 3: Japanese Patent Application Laid-open Publication No. 2005-107645    Patent Citation 4: Japanese Patent Application Laid-open Publication No. 2008-225753